Conventional methods for permanently waving keratinous fibers, particular hair, generally consist of a two stage process. Initially the hair is shampooed, and mechanically positioned into the configuration or shape desired. Generally this is acheived by wrapping the hair around cylinders (termed "rollers") of the appropriate size to either impart a curl or wave or to straighten waved hair.
In the first stage of process, referred to as the reduction stage, the disulfide linkages (S--S) of the keratin fiber are opened (reduced to two mercaptan groups), with the aid of reducing agents, including thioglycolates, sulfites, and bisulfites, etc. Depending upon the systems used, the hair is exposed either to acidic or alkaline values of pH. Thereafter, the hair is rinsed extensively and subsequently treated with a mild oxidizing agent in a second stage operation, referred to as a neutralization stage, to form new S--S linkages and to impart the desired configuration to the hair. Generally used neutralizing agents include hydrogen peroxide and sodium bromate (Robbins, Chemical and Physical Behavior of Human Hair, Van Nostrand Reinhold Company, New York (1979)).
Conventional techniques, however, have suffered from a number of disadvantages. In particular, thiol containing compositions suffer from a persistent disagreeable sulfur odor. Other compositions suffer from the irritating odor of ammonia when utilized at alkaline values of pH. Sulfite and bisulfite systems when used for "home perms" require an extensively long period of time in contact with the hair, e.g., one hour or so, and typically produce curls of less than professional standards. Additionally, since many of the other conventional ingredients are caustic to both hair and skin, safety considerations do not allow for home use formulations as concentrated as typically used in professional salons. Consequently, such "home perm" systems are not as effective, i.e., curl is not as tight and does not last as long, as available professionally. More importantly, the conventional systems tend to damage the hair (presumably through hydrolysis of peptide and amide linkages), particularly if left in contact with the hair for an extended time. The permed hair generally becomes brittle, dry, and loses agreeable tactile quality.